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Performance of 14 Pecan
Genotypes in South Alabama Baldwin and Mobile counties in Alabama lead the state in pecan production. The climate of these two counties, which border the Gulf of Mexico, is typical of other coastal regions in the southeastern United States, with high annual rainfall (165 cm), high humidity, and warm temperatures throughout a long growing season (270 days). This climate promotes the development of pecan scab (Cladosporium caryigenum), the most damaging pecan disease. Pecan growers in south Alabama must apply 8 to 10 fungicide sprays throughout the growing season on most commercial pecan cultivars to provide adequate protection from this disease. Additionally, cultivars must have at least a moderate level of genetic resistance to scab to be successful. Cultivars like ’Tejas’ and ’Wichita’ that have poor resistance to scab are not productive in this region, even with a full season fungicide program (10). On September 12, 1979, high winds from Hurricane Frederic destroyed many pecan orchards in Baldwin and Mobile counties. Orchards having cultivars with poor branch strength, like ’Desirable’, were decimated (12). Since that time, many growers have been dissatisfied with the annual production, nut quality, and disease resistance of many pecan cultivars. In 1983, a trial was established in Baldwin County at the Gulf Coast Substation (GCS), near Fairhope, Alabama, to determine the suitability of new or different pecan genotypes for commercial production in the region. Field grown pecan seedlings grafted to selected cultivars were obtained from a commercial nursery and transplanted on 12.2 m x 12.2 m spacings at GCS in February, 1983. The experiment was a randomized complete block design with four blocks and 14 test selections. Within each block, there were five adjacent trees of each cultivar, totaling 20 trees per genotype. Test selections included 12 named cultivars; ’Cape Fear’, ’Cheyenne’, ’Choctaw’, ’Davis’, ’Elliott’, ’Forkert’, ’Jackson’, ’Kiowa’, ’Maramec’, ’Melrose’, ’Stuart’, and ’Sumner’, and two unreleased selections from the USDA pecan breeding program, ’USDA 53-9-1’ (Mahan x Odom) and ’USDA 61-6-67’ (Mohawk x Starking Hardy Giant). USDA clone ’ 61-6-67’ has recently been released as ’Creek’ (14), partly due to characteristics identified in this experiment. Trees were intensively cultured, using procedures recommended by the Alabama Cooperative Extension Service (5, 8). Trees were severely pruned in early years to promote strong central leaders and wide angle branching, since the site is prone to wind damage. Nut production in early years was therefore reduced. Weeds were controlled by herbicide applications, maintaining a sod and strip orchard floor. Soil and leaf samples were taken annually, and fertilizers were accordingly applied. Fungicide applications were begun at bud break, and a full-season schedule was maintained. Insects were controlled when scouting indicated an economic injury level was present. Drip irrigation was supplied to all trees according to established recommendations for pecans (2). Data included: date of bud break, date of nut maturity, yield of each cultivar, inshell nut weight, percent edible kernel, and kernel grade percentages (percentages of #1, #2, #3, and reject kernels). Yield values reported here represent marketable yield. If percent edible kernel value for a given cultivar was less than 35% in a particular year, corresponding yields were considered unmarketable and assessed a value of zero. Nut scab ratings were made in 1994. Trunk size measurements were made in January, 1995. Date of budbreak. Mean date of budbreak for ’Stuart’ (April 6th) was later than all other cultivars. ’Forkert’, ’Maramec’, and ’Sumner’ also broke dormancy late. ’Elliott’ was earliest, with dates ranging from March 13 to March 25. The range from earliest to latest for all cultivars to break dormancy was 17 days (Table 1). Spring freezes did not occur after budbreak of any cultivars in the years when budbreak date was recorded (1990-1994). However, in the 12-year period from 1983-1994, spring freezes have occurred as late as March 22nd, which could have a negative impact on production of cultivars which commence growth early, such as ’Elliott’ and ’Cape Fear’. Nut Maturity. Nut maturity, measured in 1989-1993, varied as much as 47 days among the 14 test cultivars (Table 2). ’Elliott’ and ’Creek’ had the earliest harvest dates. Early nut maturity contributes to severe depredation from birds in coastal regions, because of low competition from other nut tree species (10). In this study, depredation from birds and squirrels was also severe on very late-ripening selections such as ’USDA 53-9-1’ and ’Jackson’, which had maturity dates as late as November 18 and November 22 (Table 2). Scab ratings. Rainfall accumulation during the seven months of pecan production (April-October) was above average in 7 out of 12 years from 1983 to 1994. The 30 year average precipitation for these months is 98.6 cm. In 1991, rainfall during this period was 126 cm, with 72 cm falling from May 1st to July 31st. In 1994, the 7 month seasonal accumulation was 101 cm, with 54 cm falling from May through July. Rainfall prohibited fungicide spraying for periods longer than 12 days in both years; consequently, incidence of scab was severe. Goff et al. (1993), rated all 14 cultivars for leaf and nut scab in August, 1991, and found differences. Differences were also found in 1994 (Table 3). ’Stuart’, ’Cheyenne’, ’Cape Fear’, ’Maramec’ and ’USDA 53-9-1’ exhibited nut scab ratings of 4 or greater (1-5 scale), despite adherence to a full-season fungicide spray schedule. ’Stuart’ and ’Cape Fear’ were considered highly resistant to scab when they were introduced to the region. Their inferior ratings support the theory that local scab isolates adapt to overcome resistance in some pecan cultivars (15). ’Elliott’, ’Sumner’, and ’Melrose’ exhibited no nut scab in 1991 or 1994, and are among cultivars reported to be highly resistant to scab (1, 10, 16). ’Jackson’, ’Davis’, ’Creek’, ’Kiowa’, ’Choctaw’ and ’Forkert’ exhibited very little scab when a full-season fungicide spray schedule was followed. We have observed over the years, however, that scab control is much more difficult in a large planting of a cultivar than in a cultivar test, and we believe that scab incidence would be higher in commercial plantings than in this experiment. Trunk size. Analysis of trunk diameter measurements made in January, 1995, revealed significant differences among cultivars (Table 4). ’Elliott’, ’Jackson’, ’Cape Fear’, and ’Forkert’ could be separated as the largest trees, while ’Cheyenne’, ’Creek’, ’Sumner’ and ’Melrose’ were the smallest, making them more suited to higher density plantings. Kernel quality and nut size. General comments among commercial pecan buyers suggest that pecans grown in south Alabama tend to be larger than average in size, but lower than average in kernel fill compared to nuts produced in other southeastern areas (J. Sasser, personal communication). Heavy rainfall during nut expansion and insufficient rainfall during kernel fill are believed to be the primary causes. In south Alabama, the period of nut sizing generally commences in early June and continues until early August, while most kernel filling is in early August and through mid-September (7). Average percent kernel across all cultivars in this study was lowest in 1989, 1993, and 1994 (Table 5). The extremely low values for 1994 were not included in means, because crop load was extremely light, shuck decline was prevalent, and damage from hickory shuckworm (Cydia caryana) was not properly prevented. Rainfall was indeed disproportionate in 1989 and 1994, favoring the nut size period (June 1- August 1). However, kernel fill was comparatively good in 1990, a year with the same pattern of rainfall. Consideration must be given to other factors known to affect pecan kernel quality, such as crop load, excess soil moisture, and reduced sunlight (13). In 1993, rainfall was evenly distributed across both nut development periods, but crop load was excessive (4). In 1988 and 1990, crop load was relatively light. Prevalence of cloud cover causing reduced net photosynthesis was not measured, but may be a major factor in south Alabama, where rainfall has been above average in 7 or 12 years since 1983. ’Forkert’ had a mean edible kernel percentage of 57, significantly higher than all other cultivars (Table 6), but 8% lower than values reported elsewhere for ’Forkert’ (12). Compared to six published cultivar trials, mean kernel percentage for ’Forkert’ at GCS ranked 5th (Table 7). Values for other test cultivars compared to these reports were likewise low, except for ’Kiowa’ and ’Sumner’. These comparisons do support comments made by commercial buyers that pecans grown in south Alabama tend to have lower percent kernel. Analysis of kernel grades shows ’Forkert’ had a significantly higher percentage of #1 kernels than other cultivars except ’Elliott’ and ’Jackson’ (Table 6). Other cultivars with high #1 grade percentages include ’Sumner’ and ’Cape Fear’. ’Elliott’ and ’Sumner’ had the lowest percentages of reject kernels, while ’Cheyenne’ had the highest. ’USDA 53-9-1’,’Choctaw’, and ’Kiowa’ had a high percentage of dark-colored, #3 grade kernels. ‘Davis’ had the poorest total edible kernel percentage, and should not be planted because of this consistent problem. The 14 cultivars encompassed a wide range of nut sizes from very small (’Elliott’) to very large (’Jackson’) (Table 6). Average nut weight of ’Davis’, ’Jackson’, ’Kiowa’, and ’Creek’ was higher in this trial compared to other reports, but ’Cheyenne’, ’Melrose’, and ’Sumner’ were not (Table 7). Nut weights of ’Cape Fear’ and ’Stuart’, two of the most common commercial cultivars in south Alabama, were average compared to other published values. Large nut size is a desirable cultivar trait in south Alabama, because of retail marketing opportunities; however, ’Elliott’ has very good local retail popularity despite its small size (6.15 g/nut). Yield. ’Kiowa’ was the most precocious cultivar, yielding 29 kg of marketable inshell nuts per ha in 1986 (4th leaf after planting), and 102 kg per ha in 1987 (5th leaf). ’Cape Fear’, ’Cheyenne’, and ’Creek’ were also precocious, yielding from 62 to 82 kg/ha in 1987. ’Elliott’, ’Stuart’, and ’Maramec’, were among the least precocious (Table 8). ’Kiowa’, ’Creek’, and ’Forkert’ were the three most productive cultivars through 12 growing seasons. These three cultivars had the highest inshell production per tree, and the highest production of kernels per tree (Table 4). Cumulative inshell production for ’Kiowa’ (1986-1994) was more than 5,100 kg per hectare. Other top yielding cultivars were ’Cape Fear’, ’Davis’, ’Choctaw’, and ’Sumner’. ’Cheyenne’ and ’Jackson’, the two least productive cultivars, yielded less than 2,000 kg per hectare (Table 8). Yield efficiency or kernel production per square cm of cross-sectional trunk area was greatest for ’Creek’, which is a very productive cultivar with small tree size (Table 4), and should be suitable to higher density plantings. Alternate bearing was exhibited early in this study by ’Kiowa’, ’Creek’, and ’Cheyenne’ (Table 8). All 24 cultivars exhibited patterns of alternate bearing similar to that experienced throughout south Alabama in recent years. In 1991 and 1993, yields were very heavy, “on-crop” years statewide, while production in 1994 was extremely low. Five cultivars; ’Kiowa’, ’Melrose’, ’Sumner’, ’Maramec’, and ’USDA 53-9-1’ had increased yields in 1992 after a large 1991 crop. With the exception of ’Maramec’, these cultivars were also able to produce small crops in 1994. Summary. Pecan cultivars must possess a combination of desirable traits to be acceptable for commercial production. In south Alabama those desirable traits include robust disease resistance, strong canopy form, good kernel quality, and annual productivity. Of the 14 cultivars examined for 12 years at GCS, all but ’Cheyenne’ demonstrated adequate resistance to pecan scab under the conditions of this experiment, given full-season use of fungicides. Many, however, were disappointing in yield and nut quality. In addition to ’Cheyenne’, ’USDA 53-9- 1’, ’Davis’ and ’Maramec’ should not be planted in this region given their poor nut quality and low yields. ’Melrose’, ’Jackson’, ’Elliott’ and ’Stuart’ additionally have not produced enough marketable inshell nuts to economically ’break even’ in a commercial orchard in south Alabama. They may be productive as older, permanent trees, if initially planted with more precocious types. ’Kiowa’, ’Cape Fear’, ’Choctaw’, and ’Creek’ demonstrated excellent precocity and yield. All four demonstrated serious alternate bearing and nut quality problems early in this trial, and are commonly known to produce lower quality nuts as tree age increases. Given these problems, a grower in south Alabama should only plant these cultivars as temporary trees or should plan to practice crop thinning. Crop load thinning with trunk shakers is an effective practice (6, 11), and should extend the economic potential of these cultivars. Two cultivars; ’Forkert’ and ’Sumner’, demonstrated a combination of good traits and deserve recommendation for planting in south Alabama. While less precocious than other cultivars, production of kernels and yield efficiency was very good (Table 4). ’Sumner’ has excellent scab resistance and has strong tree from (12). ’Forkert’ is also a strong tree, and scab incidence has been low at this location so far, but it has scabbed badly in one other southeastern cultivar trial (9). A drawback common to both cultivars is late nut maturity (Table 2) which can be a marketing disadvantage in some years. Continued testing is needed to identify pecan cultivars that possess desirable traits and can have a positive influence on pecan production in south Alabama.
Literature Cited 1. Andersen, P.C. and T. E. Crocker. 1990. Cultivar and spacing recommendations for pecans in Florida. Proc. Southeastern Pecan Growers Assn. 83:37-44. 2. Daniell, J. W. 1989. Irrigation. pp.73-85. In: W. D. Goff, J. R. McVay, and W. S. Gazaway (eds.). Pecan production in the southeast...a guide for growers. Alabama Coop. Ext. Serv. Circ. ANR-459. Auburn University. 3. Goff, W. D., L. Campbell, T. E. Thompson, J. S. Bannon, and A. J. Latham. 1993. Scab occurrence on pecan clones in Alabama in a year of high disease incidence. Fruit Var. J. 47(1):47-51. 4. Goff, W.D., N. R. McDaniel, and A. J. Latham. 1994. Influence of mechanical thinning on pecan yield an quality in the ‘on’ year. Proc. Southeastern Pecan Growers Assn. 87:157-164. 5. Goff, W. D., J. R. McVay, and W. S. Gazaway. 1989. Pecan production in the southeast...a guide for growers. Alabama Coop. Ext. Serv. Circ. ANR-459. Auburn University. 6. Goff, W. D., M. L. Nesbitt, and N. R. McDaniel. 1995. Mechanical thinning improves pecan quality and return bloom. Proc. Southeastern Pecan Growers Assn. 88:100-105. 7. Herrera. E. and W. D. Goff. 1989. Bud, leaf, and nut development. pp.3-4. In: W.D. Goff, J. R. McVay, and W. S. Gazaway (eds.). Pecan production in the southeast...a guide for growers. Alabama Coop. Ext. Serv. Circ. ANR-459. Auburn University. 8. McVay, J. R., E. Sikora, M. G. Patterson, and W.D. Goff. 1995. Commercial pecan insect, disease, and weed control recommendations. Alabama Coop. Ext. Serv. Circ. ANR-27. Auburn University. 9. O’Barr, R.D., W. B. Sherman, W. A. Young, W. A. Meadows, V. R. Calcote, and G. Ken Knight. 1989. Moreland, a pecan for Louisiana and the southeast. Louisiana Agr. Expt. Sta. Circular 129. Louisiana State Univ. Agr. Ctr. 10. Sherman, W. B., N. Gammon, and R. H. Sharpe. 1982. Pecan cultivar evaluation in north central Florida. Proc. Fla. State Hort. Soc. 95:112-114. 11. Smith, M. W., W. Reid, B. Carroll, and B. Cheary. 1993. Mechanical fruit thinning influences fruit quality, yield, return fruit set, and cold injury of pecan. HortScience 1:93-94. 12. Sparks, D. 1992. Pecan cultivars-the orchard’s foundation. Pecan Production Innovations, Watkinsville, GA. 13. Sparks, D., W. Reid, I.E. Yates, M. W. Smith, and T. G Stevenson. 1995. Fruiting stress induces shuck decline and premature germination in pecan. JASHS 120:43-53. 14. Thompson, T. E., W.D. Goff, M. L. Nesbitt, R. E. Worley, R. D. O’Barr, and B. W. Wood. 1996. ’Creek’ pecan, cultivar and germplasm releases. HortScience (in press). 15. Thompson, T. E. and L. J. Grauke. 1994. Genetic resistance to scab disease in pecan. HortScience 29(9):1078-1080. 16. Young, W. A. 1978. An update on pecan variety trials in Louisiana. Proc. Southeastern Pecan Growers Assn. 71:69-73.
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